This invention relates to a novel organic compound having a large, positive dielectric anisotropy value, which is useful as a component of liquid crystal compositions, and a liquid crystal composition containing the same.
Liquid crystal substances and their compositions have been used for various liquid crystal display elements, utilizing the dielectric anisotropy and optical anisotropy of their liquid crystal phases. Their display modes are classified into various ones such as TN type (twisted nematic type), DS type (dynamic scattering type), guest-host type, DAP type, etc. As to liquid crystal substances used therefor, a single liquid crystal compound is difficult to effect liquid crystal display in a suitable temperature range and at low operating voltages when it is filled in a cell; hence practically mixtures of several kinds of liquid crystal compounds and if required, non-liquid crystal compounds have been used to afford improved properties.
The above substances are required to be stable to moisture, heat, air, etc. Further it is desired that they be well compatible with other components used in liquid crystal compositions and the viscosity of the resulting compositions do not increase so much. Still further it is required therefor that the threshold voltage and saturation voltage necessary for driving display elements be as low as possible.
As to compounds to be contained in nematic liquid crystal substances having a positive dielectric anisotropy value, Japanese patent application laid-open No. Sho 58-83665/1983 discloses a compound expressed by the formula ##STR2## and also discloses that when nematic liquid crystal compositions containing the compound are filled in a cell, the threshold voltage lowers.
However, such liquid crystal compositions containing the compound form deposits at low temperatures. Thus, such compound is not satisfactory as a component of liquid crystal compositions.
Japanese patent application laid-open Nos. Sho 58-136680/1983, Sho 59-25872/1984 and Sho 57-142955/1982 disclose ##STR3## and a compound expressed by the formula ##STR4## respectively.
The present inventors have made extensive research in order to overcome the above-mentioned problems.
As seen from the foregoing, a first object of the present invention is to provide a novel compound useful as a component of liquid crystal compositions, which compound is well compatible with other components of liquid crystal compositions, forms no deposit in liquid crystal compositions containing it at low temperatures and when added as a component of liquid crystal compositions, the threshold voltage of the resulting compositions is reduced. A second object of the present invention is to provide a compound useful as a component of a liquid crystal composition having a lower viscosity, particularly a lower viscosity at lower temperatures as compared with those using as a component, compounds as disclosed in the prior art (such as ##STR5## A third object of the present invention is to provide a novel liquid crystal composition containing the above compound.